The invention relates generally to chemical purification. More specifically, this invention relates to the co-purification of an organic solvent and peroxide formation inhibitor to form a purified solvent mixture. The invention finds particular applicability in the preparation of solvent mixtures useful in the electronics industry.
In the semiconductor manufacturing industry, process materials used in device fabrication and their associated raw materials may be subject to contamination by peroxides such as organic peroxides. Organic solvents such as ethers and esters are particularly susceptible to organic peroxide formation in the presence of atmospheric oxygen. Among the susceptible organic solvents are ethyl lactate, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate, which are commonly used in lithographic materials. Peroxide formation in these solvents may occur during storage of the solvents or compositions containing the solvents. The presence of peroxides in lithographic materials can adversely impact the patterns being formed, for example, their thicknesses or critical dimensions. This can result in defects and yield loss in the semiconductor devices being formed. The presence of peroxides in semiconductor process chemicals can further be problematic from a safety standpoint. In particular, peroxides can pose severe fire and explosion hazards and, moreover, can be toxic and corrosive. It therefore would be desirable to minimize or eliminate the formation of peroxides in organic solvents.
In an effort to minimize the formation of peroxides in organic solvents, the addition of peroxide formation inhibitors to purified organic solvents has been proposed, for example, in U.S. Pat. No. 3,221,030. Industrial inhibitors, however, contain metallic and/or high-boiling impurities which contaminate the pure solvent. Such impurities can adversely impact semiconductor manufacturing processes and resulting electronic devices, particularly in the case of advanced semiconductor devices wherein impurity reduction is of increased importance. Methods to stabilize peroxide-forming solvents while minimizing or avoiding metallic and/or high-boiling contaminants would therefore be desired.
Accordingly, there is a need in the art for improved purification methods which address one or more problems associated with the state of the art.